Coil-forming machines of the known type are disposed at exit from a rolling line rolling metal bars or wire, and are provided with a rotary laying head, comprising at least a shaped pipe that from axial develops until it becomes partly circumferential. The product exiting from the rolling line enters into the pipe with an inlet axis coaxial with the rolling axis, and exits from the pipe with an exit axis tangent to the diameter of the coils to be obtained.
The coils thus formed are disposed by falling onto a roller-type belt, so as to be cooled and sent to the collection and/or stacking zone.
In known machines, at the end of the pipe a helical circumferential exit channel is provided which cooperates with a fixed cylindrical protection in order to stabilize the coils formed and to prevent the leading and tail ends of the rolled product from being deformed. In fact, the balance of forces at work is ensured by the presence of a drawing device. However, when the tail end of the rolled product leaves the drawing device, in particular for small products, that is, from 5 to 12 mm approximately, traveling at speeds comprised between 90 and 120 m/s, an imbalance of the forces is created, since the traction on the rolled product generated by the laying head is no longer balanced by an equal and opposite force acting upstream of the head. This imbalance in the forces determines a violent acceleration of the tail end, which is translated into a over-speed of the material with respect to the peripheral speed of the shaped pipe. Therefore, in the tail end tract of the rolled product, an omega shaped bend or curl would be formed, located on the last coil. The presence of the curl is extremely undesirable since it causes problems of jamming in the operations to collect and stack the coils; it is therefore necessary to manually eliminate the curl.
The shaped pipe and the circumferential channel are subjected to great wear due to the passing of the rolled product inside them, and due to the centrifugal force to which they are subjected.
Therefore, the helical circumferential channel is normally provided removable, both due to problems of wear and also to adapt to the sizes of the rolled product in transit.
Known helical circumferential channels are of various types, including for example those with a free width, those with a controlled width, having a control side, two control sides, with the channel open radially toward the outside, with the channel open toward the axis of rotation, etc.
For example, in WO-A-00/44512, at exit from the shaped pipe a containing ring is provided that extends as far as the exit, comprising a diverging part that accompanies, in a gradual manner, the rolled product exiting from the axial pipe toward the outside, and a terminal part with a constant section, which accompanies the coil to the exit.
In PCT/EP2006/003619 two shaped pipes are provided, which from axial become circumferential, one being offset with respect to the other by 180°.
In U.S. Pat. No. 4,242,892 it is provided that the shaped pipe that from axial becomes circumferential at least partly consists of replaceable elements, made solid with a positioning guide that defines its development as far as the circumferential part, extending for a small angle (about 50°) with a constant radius. The tract with the constant radius is not sufficient to vent the over-speed of the tail end tract and therefore does not guarantee a good conformation of the tail end coils. Moreover, this solution has a certain difficulty in assembly and dis-assembly, also because the seatings of the replaceable elements are integrated with the rotor and therefore the possible change of all the replaceable elements takes a long time. In the laying heads cited by the state of the art the pitch of the helix of the circumferential channel is fixed, and cannot be adapted to different requirements.
In WO 03/051553, which provides the possibility of working rolled products of different sizes, part of the circumferential channel consists of a plurality of guide segments with a channel open toward the outside, peripherally closed by a fixed external cylindrical protection. This solution has the main disadvantage that, in the case of small products, for example with a diameter of less than 12 mm, the size of the channel in which the product is made to pass is much bigger than the size of the product passing through, which causes the head and tail to knock against the external cylindrical protection and therefore defects to the head and tail of the product.
In document JP 2004 042123 A, as in U.S. Pat. No. 4,242,892 mentioned above, part of the shaped pipe consists of replaceable elements, but the replaceable elements, like the elements 30 in FIG. 1 of JP'123, also form part of the helical path of the rolled product, so that the part of the pipe consisting of the replaceable elements has first a growing radius, and only terminally, for an angular extension of less than about 90°, does it have a constant radius. This limited angular extension of the tract with the constant radius entails an insufficient control of the trajectory of the rolled product traveling at very high speed. Moreover, if it becomes necessary (for example to change product) to modify the pitch of the helix, the part connecting the part with the growing radius and the part with the constant radius creates difficulties in assembly and in the correctness of the alignment.
The present invention, compared with the state of the art, sets itself a plurality of purposes.
One purpose of the present invention is to obtain a guide for the rolled product in the last phase of the exit path from the laying head, which prevents or limits the traditional problems of deformation connected to the head and tail of the rolled product, especially for small products, 5-12 mm rolled at high speed, for example 90-120 m/s.
In particular, one purpose is to obtain, at exit from the laying head, a high quality rolled product with the head and tail of the coil perfectly conformed. Another purpose of the present invention is therefore to eliminate the need for the presence of an operator to intervene manually on the positioning of the heads and tails of the coils deposited on the belt, so that they do not create cobbles and therefore stoppages to the rolling process, with the corresponding losses in productivity.
Another purpose is to prevent, in particular for small diameters, the rolled product from repeatedly knocking against the walls of the containing and guide channel, thus deforming and deteriorating the final quality and increasing the wear on said walls.
Another purpose is to obtain a guide for the rolled product on all the sides thereof, as far as the exit.
Another purpose is to guide the rolled product as far as the exit from the laying head and to release the coils formed by it correctly, without creating deformations and stresses.
Another purpose of the invention is to make it easy to replace the whole or part of the guide tract of the rolled product most subject to wear.
Another purpose of the invention is to be able to easily replace the guide of the rolled product when the sizes of the rolled product change.
Another purpose is to be able to vary the value of the pitch of the helix in the terminal part of the guide for the rolled product, depending on the physical and/or technological characteristics of the rolled product.
Another purpose is to make it possible to obtain all the advantages described above also in double pipe laying heads.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.